A multi-stage gear is produced by forming a large-diameter gear and a small-diameter gear different in diameter on an outer peripheral surface of a workpiece. The multi-stage gear is used as a pinion or a sun gear mainly for use in a transmission of a vehicle. To be concrete, it is used as a gear for a transmission of an AT car, MT car, or CVT and also for an engine.
FIG. 11 shows a multi-stage gear 300 in Patent Document 1, which is a conventional art. As shown in FIG. 11, the multi-stage gear 300 includes a small-diameter gear 301 and a large-diameter gear 302, and formed with a center hole 304 through the center. Further, a gap or interval 303 is formed between the small-diameter gear 301 and the large-diameter gear 302.
The multi-stage gear 300 is produced in such a manner that a material is formed into a shape approximate to a final two-stage gear having two-staged outer periphery by hot forging in a first step. In a second step, the small-diameter gear 301 and the large-diameter gear 302 are formed by cold forging. Successively, the small-diameter gear 301 is subjected to teeth cutting by use of teeth cutting blade. For this purpose, the gap 303 has to be formed in order to avoid the blade from hitting the large-diameter gear 302.
One of the multi-stage gears is a divided gear consisting of a large-diameter gear and a small-diameter gear which are separate members. This divided gear is produced in such a way that the large-diameter gear and the small-diameter gear are made of separate members, and then they are joined together into a one-piece divided gear.